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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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CHDLDS GLACIER
405
rent With this before our eyes it was easy to see how the still larger waves during the earlier part of the summer were able to cut the river bank so easily.
The ice cliff in mid-glacier was about 285 feet high in August, 1910, parts of it having irregular projections with towers and spires of ice, and all of it being severely crevassed. A comparison of photographs of 1909 and 1910 shows that the terminus of the glacier was considerably thickened by the advance. At the time of our visit in August, 1910, the river was so low that some of the ice falls lay where they fell, though many were immediately carried away by the river. At one point at the base of the ice cliff the water was so shallow that large bowlders rose above its surface, and it was evident that undercutting was then much less active than when a deep current swept the glacier face; but it was still effective enough to cause the ice front to retreat while the glacier was flowing strongly forward. We heard many more ice falls-in the evening and night than during the day, the rumbling and roaring from the glacier increasing every night after sunset. This may possibly be due to greater contraction of the ice at night, resulting in breaking and scaling off of ice fragments, so that undercutting by the river resulted in great falls. The same increase in noises from the glacier at night was also observed at Columbia Glacier in 1910 and at Childs Glacier in 1911.
The southern border of the glacier was moderately crevassed in August, 1910, the cracks having extended throughout the lateral zone of ablation moraine and to the very edge of the glacier. There was much thickening with the advance (PI. CLI) and enough lateral spreading to cover the site of a former marginal stream, the glacier terminating close to the edge of an alder-covered bluff.
Near the northern margin of the glacier is an easily-accessible portion of the ice front, which ends upon a nearly-flat plain of till and glacial gravels, overgrown with alder and cottonwood trees 50 to 150 years old (PL CLH). Here, as in mid-glacier, the ice advanced slightly between 1900 and 1906, probably in 1905-6, but did not move forward more than a hundred feet or so along this margin. It was nearly without motion from 1906 to 1909, so that small shrubs had begun to grow upon the stagnant margin of the glacier which projected eastward only slightly beyond the main ice cliff. This part of the glacier advanced over 1600 feet between 1909 and June 3rd, 1910, and 204 feet more up to October 5th of that year, when there was a conspicuous east-projecting lobe (Fig. 59). The following table of distances from the glacier margin to the site of the northern end of the railway bridge (PI. CXLVIII, A) shows the advance of this northern lobe:
ADVANCE OF NORTHERN MABQIN OP CHILDS GLACIER TOWARD RAILWAY BRIDGE
Date	Distance from Northern Margin of Glacier to Bridge	Nature of Change
Summer,   1906	3200 feet	Slight advance since 1900
Aug.    24, 1907	3200 feet	No change appreciable
Spring,      1909	3440 feet	Slight retreat
June     3, 1910	1775 feet	Advance 1665 feet
Aug.   17, 1910	1624 feet	Advance   151 feet
Oct.     5, 1910	1671 feet	Advance    53 feet
June  16, 1911	1474 feet	Advance     97 feet